1. Field of the Invention
The present invention relates to a ceramic capacitor and manufacturing thereof, which profitably employs as a dielectric substance a reoxidated layer formed on the surface of a reduced semiconductor ceramic by reoxidating the reduced semiconductor ceramic.
2. Description of the Prior Art
Prior reduction-reoxidation type semiconductor ceramic capacitors are substantially classified into two types. One is, as illustrated in FIG. 4, adapted to heat-treat semiconductor ceramic 1 to thereby form a reoxidated dielectric layer on the surface of the semiconductor ceramic 1 as a dielectric layer 2, and thereafter dispose a pair of electrodes 3, 4 on the dielectric layer 2 in confronting relation. The other is adapted to employ as an electrode material electrode paste containing glass frit without rendering a semiconductor ceramic to a reoxidation treatment, and to diffuse in vapor phase, upon baking the electrode paste, a glass frit component contained in the electrode paste onto the surface of the semiconductor ceramic for forming a barrier layer as a dielectric layer on the surface of the semiconductor surface.
Such a reduction-reoxidation type semiconductor ceramic capacitor, which assured an extremely thin dielectric layer 2, was developed as a capacitor providing large electrostatic capacity. However, the structure shown in FIG. 4 permits the semiconductor layer 1 to be located between the electrodes 3, 4 on both sides thereof and functions as another electrode holding the dielectric layer 2 therebetween. Accordingly, the structure appears as if there exist two capacitors connected in series to each other, and hence is limited in its electrostatic capacity.
Against this, many efforts were exerted to investigate other types of reduction-reoxidation type semiconductor ceramic capacitors for the purpose of obtaining further larger electrostatic capacity. For example, there were developed those having the dielectric layer 2 only on a portion which makes contact with any one electrode 4 between a pair of electrodes 3, 4 provided on the semiconductor ceramic 1.
To be concrete, the following two types of capacitors are considered: one is, as illustrated in FIG. 5, adapted to previously heat-treat semiconductor ceramic 1 to form on the surface thereof a reoxidation layer as part of a dielectric layer 2, and remove part of the dielectric layer 2 by polishing, and furthermore to place electrodes 3, 4 respectively on the remaining dielectric layer 2 and on the semiconductor ceramic 1 exposed by the above polishing; the other is adapted to employ, upon baking the electrode 4 when forming the same, electrode paste containing metal or a metal compound serving to prevent a barrier layer from being formed on the surface of the semiconductor ceramic 1, and to render the electrode paste to baking together with the other electrode 3.
However, the former suffered from problems of, upon increasing the productivity, the increased number of fabrication processes accompanying fine polishing of the semiconductor ceramic 1 as well as increased troubles attendant on the damaged semiconductor ceramic 1. In addition, in the latter case, a barrier layer can be formed on the surface of the semiconductor ceramic 1 at the temperature of baking of the electrodes 3, 4, but it is difficult in fact to provide a sufficiently thick dielectric layer 2. For this reason there appears such a rectification effect by the action of the barrier layer that the amount of a current flowing therethrough is extremely different depending on the polarities of voltage applied between the electrodes 3, 4.